mutM, also known as formamidopyrimidine DNA glycosylase, is a base excision repair enzyme which recognizes and removes a wide range of oxidized purines from correspondingly damaged DNA. This protein is nonredundant and required to rapidly remove its substrate lesions on the chromosome. In addition, it also repaired a significant portion of the lesions recognized by Endo III, suggesting that it plays a prominent role in the global repair of both purine damage and pyrimidine damage in vivo.